OSHA Confined Spaces Quiz — 29 CFR 1926.1200-1213 Practice Questions (Subpart AA) — Page 3 of 4
Free OSHA 30-Hour Construction confined spaces practice test with 40 realistic scenarios. Permit-required spaces, atmospheric testing, ventilation, attendant duties, rescue, and entry permits with 29 CFR 1926 Subpart AA references. (Page 3 of 4)
0 / 10
Q21/ 40
A construction crew must enter a newly installed 48-inch diameter storm drain pipe that runs 300 feet between two manholes. The pipe was installed yesterday and backfilled with clean stone. No chemicals have been introduced. Does this meet the definition of a confined space?
✅ Correct Answer: B
1926.1202 defines a confined space as: (1) large enough and configured so an employee can bodily enter; (2) has limited or restricted means of entry or exit; and (3) is not designed for continuous employee occupancy. A 48-inch pipe with manhole-only access meets all three criteria. Even new, 'clean' pipes can develop hazardous atmospheres — oxygen can be displaced by soil gases (methane, CO2 from soil decomposition), or consumed by rusting/oxidation of pipe materials. 1926.1203 requires that before entry, all confined spaces be evaluated. There is no exemption for new or 'clean' confined spaces.
Q22/ 40
A welder must enter a 500-gallon water tank to repair a seam. The competent person tests the atmosphere: O2 = 20.8%, LEL = 0%, H2S = 0 ppm, CO = 0 ppm. The tank has a 16-inch manway at the top. To weld, argon purge gas will be used on the backside of the weld. The entry permit is signed. What is missing?
✅ Correct Answer: B
1926.1204(c)(2) requires that testing be conducted for the atmospheric conditions that exist or may develop. Argon purge gas, though inert and non-toxic, displaces oxygen. Being heavier than air (density ~1.38 relative to air), argon accumulates at the bottom of the confined space — exactly where the welder is working. 1926.1204(f) requires continuous monitoring when an atmospheric hazard could develop during entry. 1926.1203(e)(2)(vi) requires the permit to identify the hazards and the measures to control them — the introduction of argon as a new atmospheric hazard must be specifically addressed on the permit. This scenario is factually based on multiple fatal argon asphyxiation incidents in welding.
Q23/ 40
An attendant is monitoring a single entrant in a sewer manhole. The attendant is positioned at the manhole opening and can see and communicate with the entrant. Another worker calls for help lifting a heavy object 30 feet away. The attendant leaves to help 'just for a minute.' Is this allowed?
✅ Correct Answer: B
1926.1209(b): 'The attendant shall remain outside the permit space during entry operations until relieved by another attendant.' 1926.1209(c): 'If multiple spaces are to be monitored by a single attendant, the employer's permit program shall include the means and procedures to enable the attendant to respond to an emergency affecting one or more of the spaces without distraction.' The attendant's sole duty is to monitor the entrant — leaving for even 30 seconds is a specific and serious violation. The correct response to the lifting request: the attendant communicates to the requesting worker that they cannot leave their post, and the requesting worker must find help elsewhere.
Q24/ 40
A rescue plan for a permit-required confined space entry specifies 911 call as the rescue method. The space is a 12-foot-deep valve pit with potential H2S (hydrogen sulfide) at concentrations up to 500 ppm in upset conditions. The nearest fire department is 12 minutes away and is not trained in technical rescue. Is this rescue plan compliant?
✅ Correct Answer: B
1926.1211(b): 'The employer shall ensure that the means and procedures for summoning rescue and emergency services are operative and effective.' 1926.1211(c): 'The employer shall evaluate the response time and capabilities of the rescue service.' H2S at 500 ppm: IDLH is 100 ppm (NIOSH). At 500 ppm, loss of consciousness occurs within minutes, respiratory paralysis and death occur within 30-60 minutes. A 12-minute response (plus dispatch time, plus setup time = realistically 20+ minutes) is too slow. 1926.1211(d) requires that a rescue service be provided with access and be proficient. A fire department with no confined space rescue training is not a compliant rescue resource. On-site standby rescue is required for IDLH atmospheres.
Q25/ 40
A tank previously containing unleaded gasoline was drained and steam-cleaned once. The competent person tests the atmosphere at the manway opening at head height (5-6 feet): LEL = 0%, O2 = 20.9%, benzene = 0 ppm. The test instrument does not have a remote sampling tube, so only the opening can be tested. Can entry proceed?
✅ Correct Answer: B
1926.1204(c)(4): 'Before entry, the atmosphere shall be tested...at multiple levels (top, middle, bottom) within the space.' 1926.1204(c)(3): 'Atmospheric testing shall be conducted with equipment that has the capability to sample the atmosphere without entering.' Gasoline vapors (primarily C5-C8 hydrocarbons) are 3-4 times heavier than air — they collect at the LOWEST point. Testing only at the manway opening (5-6 feet above the tank floor) would miss a flammable or toxic layer at the bottom. A single steam cleaning may dislodge but not eliminate residue trapped in seams, scale, and pitted areas — residual hydrocarbons can outgas for hours after cleaning. A remote sampling probe is required if the atmosphere below the entry point cannot otherwise be tested.
Advertisement
Google AdSense — Responsive In-Article Ad
Q26/ 40
The entry supervisor for a permit-required confined space entry must leave the site for a family emergency mid-entry. A qualified competent person is available to take over. What is required?
✅ Correct Answer: B
1926.1203(f): 'Before the entry supervisor signs the permit to authorize entry, the entry supervisor shall verify that all tests specified by the permit have been conducted, all procedures and equipment are in place, and rescue services are available.' 1926.1203(g) requires the entry supervisor to sign the permit. 1926.1210 lists entry supervisor duties. The standard does not explicitly address mid-entry supervisor changes, but best industry practice (and OSHA interpretation) requires that the replacement supervisor: (1) verify the permit is current and conditions are unchanged, (2) confirm all entrants and attendants are briefed on the change, (3) sign the permit acknowledging assumption of the entry supervisor role. Evacuation is not required if conditions are verified unchanged.
Q27/ 40
A worker enters a trench box installed at 15 feet depth. The trench box is continuously supplied with fresh air from a blower at the surface, with the duct terminating 2 feet from the box floor. The competent person has not tested the atmosphere because the blower is running. Some workers had smelled a 'rotten egg' odor an hour earlier. Is this compliant?
✅ Correct Answer: B
1926.1204(b): 'Before an employee enters a confined space, the internal atmosphere shall be tested.' 1926.1204(c)(3): 'Atmospheric testing is required before entry into any confined space.' Ventilation is an engineering control, not a substitute for testing. H2S (hydrogen sulfide, 'rotten egg' smell) is produced by decomposition of organic material in soil, and in trenches, can accumulate from disturbed soil, sewer laterals, or landfill-adjacent sites. Importantly, H2S causes olfactory fatigue — after prolonged low-level exposure, the sense of smell is lost, so the ABSENCE of the odor does not mean the gas is gone. The competent person must test before entry regardless of ventilation status. Some deep trenches (especially boxed trenches that limit natural air circulation) may meet the definition of a confined space.
Q28/ 40
The entry permit for a permit-required confined space lists the following atmospheric conditions: O2 between 19.5-23.5%, LEL < 10%, CO < 35 ppm (TWA). During entry, the CO monitor alarm triggers at 50 ppm. The entrant is at the far end of the space. What is the required sequence of actions?
✅ Correct Answer: B
1926.1209(e): 'If the attendant detects a prohibited condition...the attendant shall: (i) Order the entrants to evacuate immediately; (ii) Summon rescue and other emergency services.' 1926.1203(h)(1): 'The entry supervisor shall terminate entry and cancel the permit when operations are completed or a condition that is not allowed under the permit arises.' 50 ppm CO exceeds the 35 ppm TWA exposure limit (1926.55 Appendix A). 1926.1204(f) requires continuous monitoring. Evacuation is mandatory when a prohibited condition arises — working faster to 'finish up' has caused multiple confined space fatalities when entrants collapse before completing evacuation. Air-purifying respirators do NOT protect against CO (CO has poor warning properties and standard organic vapor cartridges have limited CO capacity.
Q29/ 40
Three workers are assigned to enter a 100-foot long, 36-inch diameter pipeline to install a liner. There is one 24-inch manway at each end. One attendant is positioned at each manway. What specific communication method must be in place?
✅ Correct Answer: B
1926.1209(d): 'The attendant shall communicate with entrants as necessary to monitor their status and to alert entrants of the need to evacuate.' 1926.1203(e)(2)(viii): The employer's permit program must include procedures for coordinating entry operations when more than one entry point is involved. With an attendant at each end, entrants entering from opposite ends could encounter each other in the middle or a single entrant could be between attendants. If the pipe bends or the entrant's light is blocked, both attendants may lose sight simultaneously. A pre-established communication protocol between the two attendants (radio or hardline phone) is essential to maintain continuous monitoring coverage of the entire pipe length.
Q30/ 40
A subcontractor is performing abrasive blasting inside a storage tank. The blasting uses silica sand (which creates respirable crystalline silica dust). The atmosphere is tested: O2 = 20.9%, LEL = 0%. What additional testing is required specifically because of the blasting operation?
✅ Correct Answer: A
1926.1204(c)(2): 'The atmosphere shall be tested for the atmospheric conditions that exist or may develop.' 1926.1153 (Respirable Crystalline Silica) requires that for confined space abrasive blasting, the employer must assess the 8-hour TWA silica exposure. 1926.55 Appendix A lists nuisance dust limits (15 mg/m³ for total dust, 5 mg/m³ for respirable fraction). Even though O2 and LEL are acceptable, the atmospheric hazard of silica dust and total particulate in a confined space with blasting can create an IDLH condition independent of oxygen and flammability. 1926.1204(d) requires that employees be provided the opportunity to observe the testing. Testing must be done under conditions that represent actual work, not under 'clean' pre-entry baseline only.